The present invention relates to a heat-resistant thin film photoelectric converter.
Thin film photoelectric converters are used as solar cells, photo-detectors, photo-receptors for electro-photography, lasers, electro-luminescent devices, and the like. A thin film photoelectric converter contains fundamentally a layer of semiconductor and electrodes which come in contact with the layer of semiconductor. As electrodes, a transparent electrode and/or a metal electrode are used. As a material for the transparent electrode, there hitherto has been used a metallic compound such as ITO, ITO/SnO.sub.2, SnO.sub.2, In.sub.2 O.sub.3, Cd.sub.x SnO.sub.y (x=0.5 to 2, y=2 to 4), Ir.sub.z O.sub.1-z (z=0.33 to 0.5), or the like. As a metal electrode, a metal such as Al, stainless steel, Fe, Ni, Cu, brass, Zn, Ag, or the like is provided on the semiconductor.
In FIG. 2, as an example of a photoelectric converter, a typical structure of a solar cell is illustrated. A solar cell has, as shown in FIG. 2, a transparent electrode 2 of a metallic compound (e.g. a metal oxide) on a transparent substrate 1 (e.g. a glass), and thereon, a layer of p-type semiconductor 3, a layer of i-type semiconductor 4, and a layer of n-type semiconductor 5 are provided. On the layer of n-type semiconductor 5, a metal electrode layer 6 is provided as a rear electrode. Light enters the semiconductor layer through a transparent electrode and is absorbed therein so as to generate electric power. A part of the light which is not absorbed in the semiconductor layer reaches the rear electrode and is reflected back to be absorbed in the semiconductor layer.
When a conventional solar cell is used at a temperature above about 50.degree. C., a metal such as Al, Cu, brass, zinc or Ag, or metallic compound in the electrode is diffused into the semiconductor layer, so that the efficiency of the semiconductor is lowered. Especially, when an amorphous or microcrystalline semiconductor is used, the efficiency of the amorphous or microcrystalline semiconductor is notably lowered. For instance, in the case where the solar cell is used in the open air, the temperature at the surface of the solar cell reaches about 80.degree. C., so that the efficiency is remarkably lowered.
There are some metals which are not diffused into the semiconductor layer when they are used as an electrode. Examples of such metals are Cr, Ni, Fe, or stainless steel. However, those metals have the low electric conductivity or a low reflectivity compared with the above-mentioned metals such as Al, Cu, brass, Zn, and Ag. Thus, a solar cell having an electrode of Cr, Ni, Fe, or stainless steel has a drawback due to ohmic loss in the electrode or reflection loss of light at the electrode. Any type of photoelectric converter, not only a solar cell, has the disadvantage as mentioned above when used at a high temperature.
An object of the present invention is to provide a heat-resistant thin film photoelectric converter, in order to avoid the reduction in the efficiency owing to the diffusion of metal or metallic compound from the electrode into the semiconductor layer, under the condition that the ohmic loss in the rear electrode and the reflection loss of light at the rear electrode are not increased.